// Memory monitoring and leak detection
use crate::Result;
use serde::{Deserialize, Serialize};
use std::collections::{HashMap, VecDeque};
use std::sync::Arc;
use std::time::{Duration, SystemTime};
use tokio::sync::RwLock;

/// Memory allocation tracking
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MemoryAllocation {
    /// Allocation ID
    pub id: String,
    /// Size in bytes
    pub size: usize,
    /// Allocation timestamp
    pub allocated_at: SystemTime,
    /// Stack trace (if available)
    pub stack_trace: Option<Vec<String>>,
    /// Allocation type/category
    pub category: String,
    /// Whether this allocation is still active
    pub is_active: bool,
}

/// Memory usage snapshot
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MemorySnapshot {
    /// Total heap size
    pub total_heap: usize,
    /// Used heap size
    pub used_heap: usize,
    /// Free heap size
    pub free_heap: usize,
    /// Number of allocations
    pub allocation_count: usize,
    /// Largest allocation size
    pub largest_allocation: usize,
    /// Memory fragmentation percentage
    pub fragmentation_percent: f64,
    /// Snapshot timestamp
    pub timestamp: SystemTime,
}

/// Memory leak detection result
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MemoryLeak {
    /// Leak ID
    pub id: String,
    /// Leaked memory size
    pub size: usize,
    /// Duration of the leak
    pub duration: Duration,
    /// Suspected allocation category
    pub category: String,
    /// Confidence level (0.0 - 1.0)
    pub confidence: f64,
    /// Description of the leak
    pub description: String,
    /// Recommendations for fixing
    pub recommendations: Vec<String>,
    /// Detection timestamp
    pub detected_at: SystemTime,
}

/// Memory optimization suggestion
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MemoryOptimization {
    /// Optimization type
    pub optimization_type: String,
    /// Priority level
    pub priority: u8, // 1-10, 10 being highest
    /// Description
    pub description: String,
    /// Expected memory savings
    pub expected_savings: usize,
    /// Implementation difficulty
    pub difficulty: String,
    /// Implementation steps
    pub steps: Vec<String>,
}

/// Memory monitoring configuration
#[derive(Debug, Clone)]
pub struct MemoryMonitorConfig {
    /// Enable allocation tracking
    pub enable_allocation_tracking: bool,
    /// Enable leak detection
    pub enable_leak_detection: bool,
    /// Leak detection threshold (duration)
    pub leak_threshold_duration: Duration,
    /// Minimum allocation size to track
    pub min_tracked_allocation_size: usize,
    /// Maximum number of allocations to track
    pub max_tracked_allocations: usize,
    /// Snapshot interval
    pub snapshot_interval: Duration,
    /// Memory pressure threshold (percentage)
    pub memory_pressure_threshold: f64,
}

impl Default for MemoryMonitorConfig {
    fn default() -> Self {
        Self {
            enable_allocation_tracking: true,
            enable_leak_detection: true,
            leak_threshold_duration: Duration::from_secs(300), // 5 minutes
            min_tracked_allocation_size: 1024, // 1KB
            max_tracked_allocations: 10000,
            snapshot_interval: Duration::from_secs(30),
            memory_pressure_threshold: 80.0, // 80%
        }
    }
}

/// Memory monitor
pub struct MemoryMonitor {
    config: MemoryMonitorConfig,
    allocations: Arc<RwLock<HashMap<String, MemoryAllocation>>>,
    snapshots: Arc<RwLock<VecDeque<MemorySnapshot>>>,
    detected_leaks: Arc<RwLock<Vec<MemoryLeak>>>,
    monitoring_handle: Option<tokio::task::JoinHandle<()>>,
}

impl MemoryMonitor {
    /// Create a new memory monitor
    pub fn new() -> Self {
        Self {
            config: MemoryMonitorConfig::default(),
            allocations: Arc::new(RwLock::new(HashMap::new())),
            snapshots: Arc::new(RwLock::new(VecDeque::new())),
            detected_leaks: Arc::new(RwLock::new(Vec::new())),
            monitoring_handle: None,
        }
    }

    /// Create memory monitor with custom configuration
    pub fn with_config(config: MemoryMonitorConfig) -> Self {
        Self {
            config,
            allocations: Arc::new(RwLock::new(HashMap::new())),
            snapshots: Arc::new(RwLock::new(VecDeque::new())),
            detected_leaks: Arc::new(RwLock::new(Vec::new())),
            monitoring_handle: None,
        }
    }

    /// Start memory monitoring
    pub async fn start_monitoring(&mut self) -> Result<()> {
        if self.monitoring_handle.is_some() {
            return Ok(()); // Already monitoring
        }

        let allocations = Arc::clone(&self.allocations);
        let snapshots = Arc::clone(&self.snapshots);
        let detected_leaks = Arc::clone(&self.detected_leaks);
        let config = self.config.clone();

        let handle = tokio::spawn(async move {
            let mut interval = tokio::time::interval(config.snapshot_interval);
            
            loop {
                interval.tick().await;
                
                // Take memory snapshot
                if let Ok(snapshot) = Self::take_memory_snapshot().await {
                    let mut snapshots_guard = snapshots.write().await;
                    snapshots_guard.push_back(snapshot);
                    
                    // Keep only recent snapshots (last hour)
                    let cutoff = SystemTime::now() - Duration::from_secs(3600);
                    while let Some(front) = snapshots_guard.front() {
                        if front.timestamp < cutoff {
                            snapshots_guard.pop_front();
                        } else {
                            break;
                        }
                    }
                }
                
                // Detect memory leaks
                if config.enable_leak_detection {
                    if let Ok(leaks) = Self::detect_memory_leaks_background(
                        &allocations, 
                        &config
                    ).await {
                        let mut leaks_guard = detected_leaks.write().await;
                        leaks_guard.extend(leaks);
                    }
                }
            }
        });

        self.monitoring_handle = Some(handle);
        Ok(())
    }

    /// Stop memory monitoring
    pub fn stop_monitoring(&mut self) {
        if let Some(handle) = self.monitoring_handle.take() {
            handle.abort();
        }
    }

    /// Record memory allocation
    pub async fn record_allocation(
        &self,
        id: String,
        size: usize,
        category: String,
        stack_trace: Option<Vec<String>>,
    ) -> Result<()> {
        if !self.config.enable_allocation_tracking || 
           size < self.config.min_tracked_allocation_size {
            return Ok(());
        }

        let allocation = MemoryAllocation {
            id: id.clone(),
            size,
            allocated_at: SystemTime::now(),
            stack_trace,
            category,
            is_active: true,
        };

        let mut allocations = self.allocations.write().await;
        
        // Remove oldest allocations if we exceed the limit
        if allocations.len() >= self.config.max_tracked_allocations {
            let oldest_key = allocations.iter()
                .min_by_key(|(_, alloc)| alloc.allocated_at)
                .map(|(key, _)| key.clone());
            
            if let Some(key) = oldest_key {
                allocations.remove(&key);
            }
        }

        allocations.insert(id, allocation);
        Ok(())
    }

    /// Record memory deallocation
    pub async fn record_deallocation(&self, id: &str) -> Result<()> {
        let mut allocations = self.allocations.write().await;
        if let Some(allocation) = allocations.get_mut(id) {
            allocation.is_active = false;
        }
        Ok(())
    }

    /// Get current memory usage
    pub async fn get_current_memory_usage(&self) -> Result<MemorySnapshot> {
        Self::take_memory_snapshot().await
    }

    /// Get memory usage history
    pub async fn get_memory_history(&self, duration: Option<Duration>) -> Result<Vec<MemorySnapshot>> {
        let snapshots = self.snapshots.read().await;
        let cutoff = SystemTime::now() - duration.unwrap_or(Duration::from_secs(3600));
        
        Ok(snapshots.iter()
            .filter(|snapshot| snapshot.timestamp >= cutoff)
            .cloned()
            .collect())
    }

    /// Detect memory leaks
    pub async fn detect_memory_leaks(&self) -> Result<Vec<MemoryLeak>> {
        Self::detect_memory_leaks_background(&self.allocations, &self.config).await
    }

    /// Get detected memory leaks
    pub async fn get_detected_leaks(&self) -> Result<Vec<MemoryLeak>> {
        let leaks = self.detected_leaks.read().await;
        Ok(leaks.clone())
    }

    /// Generate memory optimization suggestions
    pub async fn generate_optimization_suggestions(&self) -> Result<Vec<MemoryOptimization>> {
        let current_usage = self.get_current_memory_usage().await?;
        let allocations = self.allocations.read().await;
        let leaks = self.detected_leaks.read().await;

        let mut suggestions = Vec::new();

        // High memory usage suggestion
        if current_usage.fragmentation_percent > 20.0 {
            suggestions.push(MemoryOptimization {
                optimization_type: "Memory Defragmentation".to_string(),
                priority: 8,
                description: "内存碎片化严重，建议进行内存整理".to_string(),
                expected_savings: (current_usage.total_heap as f64 * 0.1) as usize,
                difficulty: "Medium".to_string(),
                steps: vec![
                    "实施内存池管理".to_string(),
                    "优化对象分配策略".to_string(),
                    "定期进行垃圾回收".to_string(),
                ],
            });
        }

        // Large allocation suggestion
        let large_allocations: Vec<_> = allocations.values()
            .filter(|alloc| alloc.is_active && alloc.size > 1024 * 1024) // > 1MB
            .collect();

        if !large_allocations.is_empty() {
            suggestions.push(MemoryOptimization {
                optimization_type: "Large Allocation Optimization".to_string(),
                priority: 7,
                description: format!("发现 {} 个大内存分配，建议优化", large_allocations.len()),
                expected_savings: large_allocations.iter().map(|a| a.size).sum::<usize>() / 2,
                difficulty: "Hard".to_string(),
                steps: vec![
                    "分析大对象的使用模式".to_string(),
                    "实施对象池或缓存策略".to_string(),
                    "考虑延迟加载".to_string(),
                ],
            });
        }

        // Memory leak suggestion
        if !leaks.is_empty() {
            let total_leaked = leaks.iter().map(|leak| leak.size).sum::<usize>();
            suggestions.push(MemoryOptimization {
                optimization_type: "Memory Leak Fix".to_string(),
                priority: 10,
                description: format!("检测到 {} 个内存泄漏，总计 {} 字节", leaks.len(), total_leaked),
                expected_savings: total_leaked,
                difficulty: "Medium".to_string(),
                steps: vec![
                    "修复已识别的内存泄漏".to_string(),
                    "加强资源清理逻辑".to_string(),
                    "实施自动资源管理".to_string(),
                ],
            });
        }

        // Sort by priority
        suggestions.sort_by(|a, b| b.priority.cmp(&a.priority));

        Ok(suggestions)
    }

    /// Take a memory snapshot
    async fn take_memory_snapshot() -> Result<MemorySnapshot> {
        // This is a simplified implementation
        // In a real implementation, you would use system APIs to get actual memory usage
        
        // For now, we'll use placeholder values
        // In practice, you might use jemalloc stats or similar
        let total_heap = 1024 * 1024 * 100; // 100MB placeholder
        let used_heap = 1024 * 1024 * 60;   // 60MB placeholder
        let free_heap = total_heap - used_heap;
        
        Ok(MemorySnapshot {
            total_heap,
            used_heap,
            free_heap,
            allocation_count: 1000, // Placeholder
            largest_allocation: 1024 * 1024, // 1MB placeholder
            fragmentation_percent: 15.0, // Placeholder
            timestamp: SystemTime::now(),
        })
    }

    /// Background memory leak detection
    async fn detect_memory_leaks_background(
        allocations: &Arc<RwLock<HashMap<String, MemoryAllocation>>>,
        config: &MemoryMonitorConfig,
    ) -> Result<Vec<MemoryLeak>> {
        let allocations_guard = allocations.read().await;
        let mut leaks = Vec::new();
        let now = SystemTime::now();

        for (id, allocation) in allocations_guard.iter() {
            if !allocation.is_active {
                continue;
            }

            let age = now.duration_since(allocation.allocated_at)
                .unwrap_or(Duration::ZERO);

            if age > config.leak_threshold_duration {
                // Potential memory leak detected
                let confidence = Self::calculate_leak_confidence(allocation, age);
                
                if confidence > 0.5 {
                    leaks.push(MemoryLeak {
                        id: id.clone(),
                        size: allocation.size,
                        duration: age,
                        category: allocation.category.clone(),
                        confidence,
                        description: format!(
                            "长期未释放的内存分配: {} 字节，持续时间: {:?}",
                            allocation.size,
                            age
                        ),
                        recommendations: vec![
                            "检查对象生命周期管理".to_string(),
                            "确保正确的资源清理".to_string(),
                            "检查循环引用".to_string(),
                        ],
                        detected_at: now,
                    });
                }
            }
        }

        Ok(leaks)
    }

    /// Calculate leak confidence based on allocation characteristics
    fn calculate_leak_confidence(allocation: &MemoryAllocation, age: Duration) -> f64 {
        let mut confidence = 0.0;

        // Age factor
        let age_hours = age.as_secs() as f64 / 3600.0;
        confidence += (age_hours / 24.0).min(0.5); // Max 0.5 for age

        // Size factor
        if allocation.size > 1024 * 1024 { // > 1MB
            confidence += 0.3;
        } else if allocation.size > 1024 * 100 { // > 100KB
            confidence += 0.2;
        }

        // Category factor
        match allocation.category.as_str() {
            "cache" | "buffer" => confidence += 0.1, // Less likely to be a leak
            "temporary" | "scratch" => confidence += 0.4, // More likely to be a leak
            _ => confidence += 0.2,
        }

        confidence.min(1.0)
    }
}

impl Default for MemoryMonitor {
    fn default() -> Self {
        Self::new()
    }
}
